The accurate diagnosis of infection about orthopaedic implants has long been confounded by the difficulty of retrieval and detection of microorganisms. Diagnostic modalities have included white blood cell counts, erythrocyte sedimentation rates, bone scans, and C-reactive protein. Arthrocentesis with gram stain and culture has typically been the accepted standard for microorganism identification. However, the accuracy of this invasive diagnostic technique is only 80 to 85%. Thus a significant number of joint infections may be underdiagnosed and the clinical decisions, predicated on that information, will be incorrect, if only standard microbiological and serological techniques are employed. In addition, the currently available techniques are labor intensive and costly. All existing techniques suffer from a lack of sensitivity and a high false negative rate.
For situations in which time is of the essence (about 5 hours) such as trauma cases or whenever surgery cannot be planned ahead of time, and where a prosthetic device is being revised, there currently exists no procedure which can provide determinative evidence of infection, or lack thereof, in order for the surgery to properly be performed. For example, if surgery is being performed to revise a previously implanted prosthetic device, and infection was not detected by currently available techniques prior to surgery, surgery may ultimately be delayed due to infectious signs once the incision is made. In certain circumstances, a bone cement block or spacer containing antibiotics may be placed into infected tissue. The present rule of thumb among orthopaedic surgeons requires a waiting period for surgery of six weeks before removing the spacer, due to the inconclusivity of presently available techniques for determining infection. The standard culture technique has a relatively high false negative rate, largely attributed to a periprosthetic glycocalyx, and has been complicated by various antibiotic therapies which often diminish the retrieval of organisms. Furthermore, the subsequent treatment of an infected joint is performed on a purely empirical basis. Testing the efficiency of infectious therapies is largely empirical, since chronic antibiotic therapy renders standard microbiologic tests useless. Sedimentation rates have been unpredictable and may remain elevated for a lifetime, while nuclear radiographic studies are often positive for 18 months even in an uninfected joint.
There is a timely need for a new clinical technique to enhance the diagnostic accuracy of standard radiographic, serologic, and microbiologic techniques for the diagnosis of infection, particularly for infections about a joint implant. Accordingly, a technique is required which can detect the presence or absence of bacterial infection and which may be performed while intraoperative procedures are underway or very soon prior to starting. Where the results of currently available techniques are inconclusive, a procedure is also needed to provide definitive results.